1. Technical Field
The disclosure relates to an inductor and in particular relates to a three dimensional inductor.
2. Related Art
A conventional inductor with a structure as shown in FIG. 1a is a plane spiral winding inductor. The plane spiral winding inductor has some obvious drawbacks, especially, when applied in a highly dense integrated circuit, and in a high frequency integrated circuit. First, each loop of the conventional inductor is at the same plane so that a cross section area of each loop is different such that net inductance of the inductor is not easily and accurately controlled. Furthermore, the material which forms the inductor is a conductor material so that a surrounding dielectric and the conductor material will be coupled with the inductor such that parasitic capacitance is generated. Specifically, the inductor and silicon substrate material always have an intense coupling phenomenon. Because the energy consumption caused by the parasitic capacitance will increase as the frequency increases, the quality factor Q of the inductor will be lessened when operating in a high frequency.
In order to overcome the above drawback, three dimensional spiral inductors such as the inductors in FIG. 1b and in FIG. 1c have been developed. Although the coils are located at different plane, the magnetic fields generated by the windings are in the same direction. The parasitic capacitance generated by the overlapped portion of the metal wires cause the self-resonance frequency of the inductor to decrease, such that the application frequency range of the inductor is diminished. Three other dimensional spiral inductors are shown in FIG. 1d and 1e, with larger sizes and more complicated structures, which are not easily implemented in manufacturing processes.